The present invention relates to the Stretford process, which removes hydrogen sulfide from a gas stream and recovers sulfur as a by-product. More particularly, the present invention relates to a method of reducing the sulfur deposition during the absorption step of the Stretford process.
Hydrogen sulfide is a common contaminant found in sour natural gas and in tail gases from petroleum refineries. This hydrogen sulfide is noxious because it has an offensive odor, because it is poisonous, and because it is explosive in air at concentrations of as low as 4.4 volume percent.
The noxiousness of hydrogen sulfide has led to laws that severely restrict the amount of hydrogen sulfide which may be exhausted into the atmosphere. In response to these laws, numerous processes have been developed to remove hydrogen sulfide from gases. The Stretford process is one of those processes. The Stretford process is described in three patents: U.S. Pat. Nos. 2,997,439; 3,030,889; and 3,097,926.
In one embodiment of the Stretford process, hydrogen sulfide is removed from a gas stream by a sixstep process. In the first step, the gas stream is contacted in an absorber with a circulating aqueous solution to partially convert the hydrogen sulfide to elemental sulfur particles. In the second step, the solution is passed to a reaction vessel to complete the reaction. In the third step, the solution containing the sulfur particles is passed to an oxidizer. In the fourth step, that solution is oxidized in the oxidizer to form a regenerated solution. In the fifth step, the sulfur particles are removed from the regenerated solution. In the sixth step, the clarified solution is recirculated to the absorber.
Unfortunately, in this embodiment, sulfur sometimes deposits in the absorber. These deposits cause fouling of the internals of the absorber.